Lavoisier 1789 - 33 elements
Antoine Lavoisier (1743-1794) introduced the system of chemical nomenclature. His Traité Élémentaire de Chimie (1789) was the first modern chemical textbook, and presented a unified view of new theories of chemistry. In addition, it contained a list of 33 elements, or substances that could not be broken down further. His list also included light (lumière) and caloric (calorique), which he believed to be material substances. Lavoisier himself grouped them into four categories on the basis of their chemical properties:
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Dalton 1808 - 36 elements
John Dalton (1766-1844) was an English meteorologist who switched to chemistry when he saw the applications for chemistry of his ideas about the atmosphere. He proposed the Atomic Theory in 1803 which stated that
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Berzelius 1813-14 - 47 elements
As we see in the complete list of Daltin symbols, the symbol for newly discovered elements was a letter or two letters in a circle. It is therefor quite logical that a few years later, in Sweden, Berzelius suggested just using letters, argumenting those are easier to write and print.
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Mendeleev 1869 - 63 elements
Dmitrij Ivanovic Mendeleev (1834-1907) (how to spell his name? click here) had in 1869 assembled detailed descriptions of more than 60 elements and, on 6 March 1869 a formal presentation was made to the Russian Chemical Society entitled "The Dependence Between the Properties of the Atomic Weights of the Elements." Unfortunately, Mendeleev was ill and the presentation was given by his colleague Professor Menshutken. The same year, a summary of this paper was published in German in the Zeitschrift für Chemie (note). There were eight points to his presentation:
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Henry Moseley 1913
When Argon was discovered, the masses of Argon and Potassium were reversed. Henry Moseley found the reason for these apparent exceptions to the rule. As a result of Moseley's work, the periodic law was revised. He stated that physical and chemical properties are a periodic function of their atomic number, rather than mass. This better explained the gaps in the table. The atomic number of an element indicates the number of protons in the nucleus of each atom of the element. The atomic number also indicates the number of electrons surrounding the nucleus. Herewith he created the modern periodic table in which each succeeding element has one more proton and electron than the former element.
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